Certain additive manufacturing techniques such as three-dimensional printing use thermoplastics or the like that can be deposited in a heated, liquid form and then cooled to provide a resulting solid structure. Some systems use a heated build chamber in order to mitigate thermal stresses and other difficulties that arise from the thermal expansion and contraction of build materials during fabrication. While the heated build chamber usefully regulates the thermal environment for a build process, there is typically a significant amount of heating inefficiency, particularly early in the fabrication process when only a small amount of build material requires any thermal management. There remains a need for improved heating techniques that direct initial heating toward the region(s) in a build chamber where a build will be initiated.